Licensed gun dealers already can't sell guns to buyers who answer "yes" when a required form asks them if they are "an unlawful user of, or addicted to," marijuana or other controlled substances.

A Sept. 21 letter from the Bureau of Alcohol, Tobacco, Firearms and Explosives also says dealers can't sell a gun or ammunition if they have "reasonable cause to believe" the buyer is using controlled substances, even if the state allows it.